This invention relates to freeze dryers, and more particularly to method and means for preventing possible contamination of a freeze dryer chamber and the freeze dried product by the operating cylinder rod.
Freeze drying equipment includes a chamber in which a plurality of spaced apart shelves supporting vials or other containers to be stoppered, are moved toward and away from each other by operation of an elongated piston rod which is connected at its inner end to a header within the freeze drying chamber and at its outer end to a piston which is reciprocative in an elongated hydraulic cylinder mounted outside the freeze drying chamber.
It has long been suggested, without practicable solution, that contamination may be introduced into the freeze drying chamber by the piston rod. The only known effort to eliminate this possibility is disclosed in U.S. Pat. No. 3,286,366 in which it is proposed to replace the cylinder and piston rod with a sealed, expandable air bellows or bladder contained within the freeze drying chamber. Although this arrangement may be effective for a small, single shelf freeze dryer, as is disclosed in the patent, it is not operable for the large, multiple shelf freeze dryer systems with which the present invention is concerned, since the pressures and movement distances involved require the use of rather long hydraulic cylinders and piston rods operated at substantially greater pressures than are available with air bellows.